Electric Systems Chapter 1 part 2

What circuit fault can result in an arc flash?

An arcing fault

Explain what is meant by an arcing fault

An arcing fault is an unintentional arcing condition in a circuit typically between the conductors in a frayed extension cord, arcing between a hot conductor and ground, or arcing in a loose connection in either the hot or neutral conductor.

When lifting a load, why is it important to lift with your legs and not your back?

Bending from the waist rather than the knees applies ten times the pressure to your lower back.

How often is the National Electrical Code updated and published?

The NEC (National Electrical Code) is updated once every three years

What is the primary purpose of the rules set forth in the National Electrical Code.

The National Electrical Code (NEC) comprises a set of rules that, when properly applied, are intended to provide a safe installation of electrical wiring and equipment.

A ladder is used to reach the top of a building 16 feet tall. According to the 4-to-1 ratio rule, what distance should the bottom of the ladder be placed from the side of the building

The base of the ladder should be placed 1 foot away from the wall for every 4 feet of vertical height to the point of support

in general, voltage levels above what value are considered dangerous?

30 Volts

What are the deck requirements for a scaffold work platform?

Scaffolds must be erected on rigid footing that can carry the maximum intended load using only materials designed and marked for this purpose. Guardrails and toe boards must be installed on the open sides and ends of platforms that are higher than 6 feet above the ground or floor. Work platforms must be completely decked with scaffold planks extended over their end supports not less than 6 inches nor more than 12 inches and must be properly blocked. Keep scaffold platforms clear of unnecessary material.

A fall arrest system must be rigged so that workers cannot free-fall more than how many feet?

6 feet

How does a ground-fault circuit interrupter (GFCI) sense ground-fault current?

A GFCI actively compares the current going to and coming from equipment in the grounded neutral and ungrounded hot lines, so that if current becomes unequal on one side due to a fault it can break the current flowing out.

Assume a piece of electrical equipment has been listed by the Underwriters Laboratories. What does this indicate?

A UL listed product indicates the piece of electrical equipment or material has been tested and evaluated for the purpose for which it is intended to be used.

What is a permit-required confined space

A confined space with health and safety hazards associated with it.

Explain what is meant by a ground fault.

A ground fault is defined as an unintentional, electrically conducting connection between an ungrounded conductor of an electric circuit and the normally non-current-carrying conductors, metallic enclosures, metallic raceways, metallic equipment, or earth.

Compare what GFCIs and AFCIs protect against.

AFCIs are intended to reduce the likelihood of fire caused by electric arcing faults, whereas GFCIs are personnel protection intended to reduce the likelihood of electric shock hazard.

What does a lockout-tagout procedure refer to?

Electrical lockout is the process of removing the source of electric power and installing a lock, which prevents the power from being turned ON. Electrical tagout is the process of placing a danger tag on the source of electric power, which indicates that the equipment may not be operated until the danger tag is removed.

In general, current levels above what value are considered dangerous?

0.005 A or 5 mA

Explain why an arc flash is so potentially dangerous

An arc flash can burn with temperatures that exceed 35,000°F as well as release blinding ultraviolet light, toxic gases, and damaging acoustic waves.

Which classes of fire are multipurpose dry-chemical fire extinguishers approved for?

Class A, B, and C fires

List four hazardous properties or characteristics.

Corrosive, flammable, toxic, reactive

Why is the earth not considered to be an effective path for ground-fault current?

Earth may be too poor a conductor to properly trip overcurrent protection devices, resulting in a potentially lethal energized system.

What does the term personal protective equipment (PPE) refer to

Protective equipment used to protect oneself from dangerous or hazardous conditions.

Compare the terms grounding and bonding.

Grounding is the intentional connection of a current carrying conductor to the earth, while bonding is the is the permanent joining of metal parts that aren't intended to carry current under normal operation.

What is the approximate current at which a GFCI will operate to open the circuit?

Most GFCIs will detect and break leakages as small as 5mA in 1/40th of a second

What personal protective attire is required when taking measurements on energized circuits?

Required protective attire may include: non-metal hard hats, safety shoes, goggles or other eye and face protection, cotton uniforms tightly fitted around the sleeves and trouser legs, and insulated gloves.

Compare the amount of current that results from series and parallel arc faults.

The series configuration means the arc current cannot be greater than the load current the conductor serves. The parallel arc fault, which can occur as a short circuit or a ground fault can far exceed a series fault.

Does the severity of an electric shock increase or decrease with each of the following changes? a. A decrease in the source voltage. b. An increase in body current flow. c. An increase in body resistance. d. A decrease in the length of time of exposure

a. decrease b. increase c. decrease d. decrease

Define each of the following terms associated with an arc flash: a. Bolted fault b. Arcing fault c. Arc blast

b. arcing fault C. Arc Blast

When should face shields be worn

Face shields should be worn during all electrical switching operations where there is a possibility of injury to the eyes or face from electric arcs or flashes or falling objects that may result from an explosion.

What is the main goal of OSHA?

OSHA's main goal is to ensure that employers provide each of their employees a place of employment that is free of recognized hazards.

As part of a lockout-tagout procedure, you are required to open a disconnect switch. What is the safest way to proceed?

Open the main disconnect switch (do not operate if the switch is still under load). Stand clear of the box, and face away while operating the switch with the left hand (if the switch is on the right side of the box).

List the three ingredients required to sustain a fire.

Oxygen, heat, and fuel.

List three reasons for employing proper grounding practices

To limit the voltage surges caused by lightning, utility system operations, or accidental contact with higher-voltage lines, to provide a ground reference that stabilizes the voltage under normal operating conditions and to facilitate the operation of overcurrent devices such as circuit breakers and fuses under ground-fault conditions.

A voltmeter is used to verify that no voltage is present after the lockout-tagout procedure has been completed. Explain how you can ensure that the voltmeter is working properly.

You perform a live dead live test to ensure a voltmeter is working properly by first testing it against a known live voltage source within the same range voltage as the circuit you will be working on. Then checking the presence of voltage on the equipment you have locked out. Finally, you will check it again against the known live source.